1. Field of the Invention
The present invention relates generally to textile cords for pneumatic tires and more specifically to cords for belts of radial carcass tires for heavy duty use.
2. Description of the Related Art
Radial carcass tires, especially off-the-road tires and heavy duty off-the-road tires have typically 1 to 5 carcass plies, 2 to 6 belt plies and one to four sets of beads.
Off-the-road tires, because of the nature of their use, are exposed to cutting and delamination caused by sharp rocks and uneven terrain. This problem is addressed by providing such tires with belts reinforced with high strength material.
One reinforcement cord currently used in belts of heavy duty industrial tires is composed of 3 yarns of aramid, having a linear density of 1500 Denier, the yarns and the cord being twisted at 6.9 turns per inch (TPI). Such cord has a strength of about 750 N. Aramid is high cost to manufacture and to process.
Another reinforcement cord currently used in belts of agricultural tires is composed of 2-3 yarns of rayon, having a linear yarn density of 1650 to 2200 Denier, the yarns and the cord being respectively twisted at about 9 TPI and 6.5 TPI. Such cords have strengths of about 180 N and 350 N respectively. This cord is high cost to manufacture because of high material cost, and the cord is subject to moisture pick-up and the cord has a low tenacity.
Polyester cords, such as 2.000/2 6/6 or 1.000/2 12/12 TPI which have respectively twist multipliers of 5.2 and 7.35 are also currently used to reinforce belt plies of farm tires. The high twist levels of between 6 and 12 TPI, however, do not take full advantage of the dimensional stability, the modulus, the shrinkage, and the tensile strength of the polyester material. The material cost for this material is also high.